The invention relates to a process for the manufacture of screen components of various lengths for system screening decks that are fabricated of a weldable plastic material subdivided into short components having a square or rectangular basic shape, and long components whose length is two or more times that of said basic shape, each screen component including supporting members that are provided with fastening elements or fastening recesses.
It is known to manufacture such screen components for system screening decks by the open casting process. In this process, liquid plastic is filled from above into open moulds, manual or mechanical casting devices being used and the casting material being processed under atmospheric pressure. The reusable open moulds are of relatively simple design, and their dimensions correspond to the short and long components.
Furthermore, it is known to manufacture such screen components by the injection moulding process, the liquid plastics material being pressed into a closed injection mould under pressure. Injection moulds, which have to be separable for removal of the finished workpiece, require runners and venting channels and must be adapted to the particular injection moulding machine, are many times more expensive than the moulds open on one side which are necessary for the open casting process. Since here too a separate mould is required for each size of screen component, it is endeavoured to keep down the number of screen components of different lengths, to reduce accordingly the expenditure on injection moulds. In addition, 21/2 times the length of a square basic shape of the screen components is not exceeded, as the amounts injected and clamping forces of the injection moulding machines usually used are insufficient for screen components which are any longer.
The present invention in contrast to the foregoing, provides a process of generic type by which the screen components can be manufactured in various lengths of injection-moulded quality for which only one injection mould of a single format corresponding to the basic shape and a relatively small injection moulding machine are necessary.
It is known in principle, from German Utility Model No. 6,915,606, to manufacture a plate screening deck or a screening mat of prefabricated screen mouldings or individual plates welded to one another. In this prior art arrangement, the screen mouldings are already connected to one another by a butt welding process, a welding being provided both on the longitudinal sides and on the transverse sides of the screening mouldings. However, welded screening mats are not intended or suitable for use in system screening decks; in particular, the prior art arrangement has no concern with the problem of maintaining a specified modular dimension with scree components of various lengths and also of safe-guarding a constant, in each case system-dependent pitch of the fastening elements to the screen components. Furthermore, only screen components of the same format are ever used, so that there is no need for a distinction between short components and long components. By the known method, therefore, the scree components can be welded to one another straight away as blanks.